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In humans, the left side of the brain usually controls speech and language, and the right side controls emotion. In left-handers, however, this pattern is often reversed. In a similar way, people with schizophrenia often have unusual patterns of brain asymmetry.

The leader of the study, Dr Clyde Francks of the Wellcome Trust Centre for Human Genetics, said: "People really should not be concerned by this result. There are many factors which make individuals more likely to develop schizophrenia and the vast majority of left-handers will never develop a problem. We don't yet know the precise role of this gene."

There is also evidence that asymmetry of the brain was an important feature during human evolution. Apes' brains are more symmetrical than humans' and they do not show a preference for using either the right or left hand.

Dr Francks added: "We hope this study's findings will help us to understand the development of asymmetry in the brain.

"Asymmetry is a fundamental feature of the human brain that is disrupted in many psychiatric conditions."